1. Field of the Invention
The present invention relates to a transmission for an all-terrain vehicle, including a variable-speed drive, such as a variable-speed belt-drive mechanism, and a gear transmission mechanism.
2. Description of the Related Art
In an all-terrain vehicle of above-mentioned type, a gear transmission mechanism combined with a variable-speed drive usually provides a forward high-speed ratio, a forward low-speed ratio, neutral and reverse. While the all-terrain vehicle is traveling, the gear transmission mechanism is usually placed in the forward high-speed ratio and the variable-speed drive changes speed automatically. When the condition of the road requires or when necessary, the vehicle is stopped temporarily, and the gear transmission mechanism is placed in the forward low-speed ratio or reverse.
Transmissions for an all-terrain vehicle, capable of being selectively placed in a forward high-speed ratio, a forward low-speed ratio, neutral or reverse by operating a single shifting lever are disclosed in JP-A Nos. Hei 8-337131 and Hei 2-203079, respectively.
FIGS. 17 and 18 show an all-terrain vehicle with the transmission disclosed in the former publication. As shown in FIG. 17, a single, L-shaped shifting lever 301 is supported on an engine 302. The shifting lever 301 extends laterally from the engine 302 to the right and rises upward. As shown in FIG. 18, the shifting lever 301 is connected with a first lever mechanism 305 for selecting a forward speed, neutral or reverse, and a second lever mechanism 306 for selecting a forward high-speed ratio or a forward low-speed ratio. The lever mechanisms 305 and 306 extend toward a middle part of the engine 302 with respect to width. Rods 307 and 308 or wires are connected to the lever mechanisms 305 and 306, respectively. Thus the single shifting lever 301 is connected to a shifting fork for selecting the forward speed, the neutral or the reverse, and a shifting fork for selecting the forward high-speed ratio or the forward low-speed ratio by the lever mechanism 305 and the rod 307, and the lever mechanism 306 and the rod 308, respectively. Gate plate 309 provided with H-shaped guide slots for guiding the shifting lever 301 is disposed on one side of a body.
FIG. 19 shows an all-terrain vehicle provided with the transmission disclosed in the latter publication. A single bent shifting lever 401 is disposed on one side of an engine 402 so as to project laterally outward. The shifting lever 401 is interlocked with a cam drum (change drum) 406, as a shifting fork driving member. The cam drum 406 is held in an upper part of the interior of a transmission case 405. The cam drum 406 is turned to operate two shifting forks.
Both the transmissions can be selectively placed in the forward high-speed ratio, the forward low-speed ratio, the neutral or the reverse by operating the single shifting lever. Since the shifting lever 301 of the former transmission shown in FIGS. 17 and 18 is supported on the engine 302 and projects to the right, the shifting lever 301 places a restriction on a space in which a rider's leg can be placed. Accordingly, riding quality of the vehicle is degraded. The shifting lever 301 needs to be moved horizontally and vertically along the H-shaped guide slots of the gate plate disposed on one side of the body and is not easy to operate.
Since the rods 307 and 308 connecting the shifting lever 301 to the shifting forks held in the transmission case are extended near the middle part of the engine 302 with respect to width, work for installing the rods 307 and 308, and adjusting the length of the rods 307 and 308 takes much time.
Since the two rods 307 an 308 are necessary for selecting the forward high-speed ratio or the forward low-speed ratio, and for selecting the forward speed, the neutral or the reverse, a wide space is needed to place the two rods 307 and 308. Therefore, the arrangement of various parts, for example an air cleaner, in a space around the middle part of the engine 302 is restricted.
The latter transmission mounted on the all-terrain vehicle shown in FIG. 19 has the transmission case 405 and the cam drum 406 held in the transmission case 405. Therefore a large space must be available in the transmission case 405 for holding the cam drum 406 therein and hence the transmission case 405 is inevitably large. Since the single cam drum 406 operates the two shifting forks, complicated mechanisms must be held in the transmission case 405 and hence the transmission is costly. The shifting lever 401 disposed at a lower position on one side of the body limits a space in which a driver's leg can be placed.
When the gear transmission mechanism of the all-terrain vehicle is placed in the reverse or the neutral, it is necessary to detect the gear position of the gear transmission mechanism and to indicate the gear position by a pilot lamp or the like for the rider.
Usually, the shifting mechanism of a conventional all-terrain vehicle includes a shifting rod, a change drum disposed near the shifting rod. The change drum is turned to move a shifting sleeve by a shifting arm interlocked with the shifting rod by the cam groove or the like of the change drum to place the transmission in a desired gear ratio. A gear position detector for detecting the reverse position and the neutral position is mounted on the change drum and detect the reverse position and the neutral position corresponding to the angular positions of the change drum, respectively.
Another conventional shifting mechanism disclosed in JP-U No. Hei 2-27061, which is different from the foregoing shifting mechanism having a change drum, is not provided with any change drum. A gear position detecting device included in this shifting mechanism includes a shifting rod provided with depressions, a detecting pin extended in the direction of the diameter of the shifting rod so as to be in contact with the depression of the shifting rod, and a gear-position detecting switch. The gear-position detecting switch detects the gear positions of the transmission from the axial position of the detecting pin.
The former shifting mechanism having a change drum needs a large space for holding the change drum therein, and the detecting switches for detecting the neutral and the reverse position must be mounted on the change drum. Consequently, the shifting mechanism is unavoidably large.
The gear-position detecting switch of the latter shifting mechanism is disposed at a position corresponding to a middle part of the length of the shifting rod. Since various parts are arranged around the gear-position detecting switch, work for installing the gear-position detecting switch takes much time. Work for accurately forming the depressions in the surface of the shifting rod needs much time.